Two types of physiological rhythmic activity are conventionally studied and measurable. One type of physiological rhythmic activity is heart rate variability (“HRV”). HRV is believed to be based on the fluctuations of the activity in brain cardiovascular vasocontrictory and vasodilatory centers. Typically, these fluctuations are a result of blood pressure oscillation (baroreflex modulated), respiration (parasympathically mediated via thermoregulatory peripherical blood flow adjustment) and circardian biorhythm. All these factors can influence the length of beat-to-beat intervals, named cardiointervals or R—R intervals.
Of note, cardiointervals are typically measured from electrocardiogram (“ECG”), plethysmogram, or phonocardiogram, but predominantly an ECG is used. The frequency of such measurements is typically directly associated with cardiac impulse frequency of around 1 Hz.
In this regard, examples of patents relating to such ECG's include the following: U.S. Pat. No. 4,006,737 to Cherry (entitled “Electrocardiographic Computer”); U.S. Pat. No. 4,073,011 to Cherry et al. (entitled “Electrocardiographic Computer”); U.S. Pat. No. Re. 29,921 to Cherry et al. (entitled “Electrocardiographic Computer”); U.S. Pat. No. 4,090,505 to Mortara (entitled “Electrocardiographic Recording Method And Means”); U.S. Pat. No. 4,098,267 to Stein et al. (entitled “System For Display And Analysis Of Physiological Signals Such As Electrocardiographic (ECG) Signals”); U.S. Pat. No. 4,216,780 to Rubel et al. (entitled “Apparatus For The Acquisition And Pre-Processing Of Electrocardiographic Data”); and U.S. Pat. No. 4,341,225 to Gallant et al. (entitled “Electrocardiography System”).
Moreover, examples of patents relating to numeric processing of ECG signals (i.e., by fast fourier transform (“FFT”)) include the following: U.S. Pat. No. 4,680,708 to Ambos et al. (entitled “Method And Apparatus For Analyzing Electrocardiographic Signals”); U.S. Pat. No. 4,924,875 to Chamoun (entitled “Cardiac Biopotential Analysis System And Method”); U.S. Pat. No. 4,947,857 to Albert et al. (entitled “Method And Apparatus For Analyzing And Interpreting Electrocardiograms Using Spectro-Temporal Mapping”); U.S. Pat. No. 5,025,794 to Albert et al. (entitled “Method For Analysis Of Electrocardiographic Signal QRS Complex”); U.S. Pat. No. 5,029,082 to Shen et al. (entitled “Correlative Analysis In Multi-Domain Processing Of Cardiac Signals”); U.S. Pat. No. 5,117,833 to Albert et al. (entitled “Bi-Spectral Filtering Of Electrocardiogram Signals To Determine Selected QRS Potentials”); U.S. Pat. No. 6,223,073 to Seegobin (entitled “Noninvasive Method For Identifying Coronary Disfunction Utilizing Electrocardiography Derived Data”); and U.S. Pat. No. 6,678,547 to Carlson et al. (entitled “Cardiac Rhythm Management System Using Time-Domain Heart Rate Variability Indicia”).
Another type of physiological rhythmic activity is the electric field of the human brain. The electric field of the human brain is typically measured by an electroencephalogram (“EEG”). Normally, the frequency spectrum includes a number of neuronal activation amplitudes defined as delta 0.5–3 Hz, theta 4–7 Hz, alpha 8–13 Hz, beta 14–30 Hz and gamma >30 Hz (within about 100 Hz).
By way of additional background, it is noted that the number of nerve cells in the brain has been estimated to be on the order of 1011 and that cortical neurons are strongly interconnected. Further, the electric behavior of the neuron corresponds to the description of excitable cells. It is believed that generally, the resting voltage is around −70 mV, and the peak of the action potential is positive. Moreover, it is believed that the amplitude of the nerve impulse is generally about 100 mV, and it lasts about 1 ms. Spontaneous activity is conventionally measured on the scalp or on the brain via EEG. Evoked potentials are those components of EEG that arise in response to a stimulus (which may be electric, auditory, visual, etc.). Such signals are typically below the noise level and thus not readily distinguished. Single-neuron behavior can conventionally be examined through the use of microelectrodes, which impale the cells of interest.
In any case, examples of patents relating to such EEG's include the following: U.S. Pat. No. 3,934,267 to Kosaka et al. (entitled “Vital Phenomenon Recording And/Or Reproducing Device”); U.S. Pat. No. 4,308,873 to Maynard (entitled “Electroencephalograph Monitoring”); U.S. Pat. No. 4,421,121 to Whisler et al. (entitled “Method And Apparatus For Obtaining A Non-Cephalic Referential Electroencephalograph”); and U.S. Pat. No. 5,241,967 to Yasushi et al. (entitled “System For Evoking Electroencephalogram Signals”).
Moreover, examples of patents relating to numeric processing of EEG signals (i.e., by fast fourier transform (“FFT”)) include the following: U.S. Pat. No. 4,583,190 to Salb (entitled “Microcomputer Based System For Performing Fast Fourier Transforms”); U.S. Pat. No. 4,736,307 to Salb (entitled “Microcomputer-Based System For The On-Line Analysis And Topographic Display Of Human Brain Electrical Activity”); U.S. Pat. No. 5,083,571 to Prichep (entitled “Use Of Brain Electrophysiological Quantitative Data To Classify And Subtype An Individual Into Diagnostic Categories By Discriminant And Cluster Analysis”); U.S. Pat. No. 5,092,341 to Kelen (entitled “Surface ECG Frequency Analysis System And Method Based Upon Spectral Turbulence Estimation”); U.S. Pat. No. 5,109,862 to Kelen et al. (entitled “Method And Apparatus For Spectral Analysis Of Electrocardiographic Signals”); U.S. Pat. No. 5,813,993 to Kaplan et al. (entitled “Alertness And Drowsiness Detection And Tracking System”); U.S. Pat. No. 6,549,804 to Osorio et al. (entitled “System For The Prediction, Rapid Detection, Warning, Prevention Or Control Of Changes In Activity States In The Brain Of A Subject”); U.S. Pat. No. 6,574,491 to Elghazzawi (entitled “Method And Apparatus For Detecting A Physiological Parameter”); and U.S. Pat. No. 6,574,573 to Asano (entitled “Spectrum Analysis And Display Method Time Series”).
Nevertheless, the above-mentioned patents fail to disclose use of the time series/frequency-domain regions employed by the present invention (e.g., for distinguishing an individual).
Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof.